1. Field of the Invention
This invention relates to high precision numerical data processing, and more particularly to high speed optical analog-to-digital conversion.
2. Background of the Invention
For high precision numerical data processing, digital (rather than analog) computation is preferred. To increase the data processing rate, both fast signal processing and fast analog-to-digital (A/D) conversion are required. Optical A/D conversion has been investigated as an alternative to semiconductor or superconductor based A/D conversion. Wide-band, fast optical A/D conversion based on electro-optic (E-O) waveguide interferometric devices has been proposed. Recently, optical A/D conversion based on an optical logic gate array and an optical table look-up processor has been proposed.
Optical A/D conversion based on an optical theta-modulation and table look-up (TMTL) has also been proposed. The concept of using TMTL for signal processing has been known for decades, and the TMTL concept has been implemented by deflecting an electron-beam between deflection plates in an oscilloscope. When used in a video display, the resultant device could reach over 1000 resolvable levels.
The TMTL concept has also been implemented by an optical theta-modulation based on a variable grating mode (VGM) liquid-crystal (LC) device for optical signal processing. Such a VGM LC has also been proposed for the optical implementation of optical logic and signal processors. However, such a device has serious problems, such as a limited dynamic range and a limited switching time, which have inhibited high speed applications.